I need to wire a Range Receptacle in the USA for 4 wires currently 3 wires are run to the range ( a renovation is being done and the new range will be in a different location). I am not sure at the moment on the exact sizing that is there and whether or not it was correctly done. I am wanting to simply pull a single wire from panel to range receptacle in order to get the 4th wire.

1: Is this acceptable, or does the wire need to be in a jacketed cable bundle or inside a conduit?

2: If I must pull all 4 new; I intend to pull 6/3 for a 50AMP circuit, this should be sufficient to cover the gambit of Electric Ranges. I do believe that the new range will be 40 AMP, but thinking the added wire size will be better all around. I know 8/3 is cheaper, does code force the 6/3 wiring?

What is the correct way to do this ?

I do know that people use Aluminum wiring at larger wire size - as it is cheaper but think the issues of galvanic corrosion and breaker compatibility etc might be too much hassle..

  • Depends very much on what you have NOW for wire to the 3-wire. If it's 2 hots and a braided neutral/ground then you need all new wires. If it's 3 insulated conductors, you MAY be able to just add a ground wire. If it's in metallic conduit (rare but not unheard of) you may already have a ground. Aluminum wire is more compatible with your breakers' terminals than copper is, actually, so that's just Fear, Uncertainty, and Doubt from a fiction. Aluminum feeders of this size have never been an issue - only the 10/12Ga from poorly chosen alloys for 15/20A circuits was a problem.
    – Ecnerwal
    May 31 at 15:48
  • The house was built mid 80's I suspect 2 hots and a bare metal neutral / ground - just a suspicion. I can assume no conduit pipe in this house , just looking at other wiring.
    – Ken
    May 31 at 15:57
  • Well, nothing like looking at it (at the main breaker panel may be easier if the far end is difficult until you start tearing kitchen apart) - at that age you MIGHT get lucky and find a /3 cable with ground, but connected to the outdated outlet style.
    – Ecnerwal
    May 31 at 16:05
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    @ThreePhaseEel no I can't - I will have to pull out the slide in which is mounted in the cabinets .. and I have been doing preliminary. When I am there again - I will check the far end in the panel . to see what wiring is there. know the breaker size but that does not tell me wire gauge and wires ..
    – Ken
    May 31 at 16:23
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    @Ken -- if you can give us a photo of where the run for the range exits the panel, we can work from that instead May 31 at 17:23

First, is the existing cable any good?

Aside from the obvious material condition of the wire...

Here's how "grandfathering" works. It is legal to continue an installation in service if it was legal when initially installed.

  • all-insulated (white black red) no-ground NM cable was legal
  • Service Entrance type (2 insulated blacks + a mesh neutral) was legal.

You were meant to switch to 3-wire+ground as soon as your supplier ran out of 3-wire/no-ground. Unfortunately what some people did was switch to 2-wire+ground (black white bare), and misuse the bare wire for neutral. That was never allowed. So if that's your cable, you can't use it. Leave it in the walls, since it CAN be used for a "separates" rangetop that does not require neutral. If someone installs "separates" range/oven, they'll thank you for leaving it there.

Ovens need neutral for the oven light. Back when incandescents were the only light, everybody had a drawer full of 120V ones, and oven builders wanted you to be able to just use those. That's moot nowadays since LEDs burn up in ovens.

The upshot is, if the cable isn't any good, it's a moot question - you'd need to replace it anyway.

Yes, retrofitting ground is allowed...

The wire currently in your 3-wire feed is neutral, not ground. Even if it is the bare mesh of SE cable, it is still neutral. (service entrances don't have ground).

A #10 ground wire can be retrofit via any reasonable route, and it doesn't even need to go back to the panel - it can reach any of

  • a junction box with non-bendable metal conduit back to the panel
  • a junction box with #10 or larger ground wire back to the panel
  • straight to the Grounding Electrodes, the ground wires between panel and water pipe/ground rods. (note this cannot be cut; you use a split bolt).

... however, maybe not retrofitting and extension

To begin with, the extension would require a splice. The splice must occur inside a large-enough junction box, and the cover of the box must remain accessible forever without needing tools to disassemble any part of the building. It can be in the back of a kitchen cabinet if it's reachable for maintenance; it cannot be blocked in by a kitchen cabinet. So any solution that renders the splice outside a box, in a too-small box, or in an inaccessible box is a deal killer.

Second, the AHJ (local inspector) has to be OK with a retrofit as part of an extension. This is, at best, a gray area, and the inspector could rule either way, and knock you on your socks! I would run it by them before committing to it.

You can use a cable, but conduit is better

The absolutely ideal situation for this is a conduit running back to the panel. That would allow you to fit any appropriate wires at any time, so it makes it easy to, say, put in a 50A all-in-one and fit dual 30A separates later. It would also economize, because with the individual THHN wires used inside conduit, #8 copper THHN is good for 50A.

If you're willing to fit conduit, you'll thank yourself later. Non-flexible metal conduit will take care of grounding as well, but is somewhat more difficult to fit. 3/4" conduit should satisfy all requirements. The conduit must be installed, adequately stapled down and complete before any wires are pulled in; this often frightens novices but it really is the easier way to do it.

But feel free to use cable if that is easier.

NM and UF cables have current limitations

They are the "shoemaker's sons" of electrical cable, having a lower ampacity than their "big brother" cables (of every other type).

  • #8 NM/UF is only good for 40A. #8 anything else is good for 50A.
  • #6 NM/UF is only good for 55A. #6 anything else is good for 65A.
  • #6 aluminum has the same ratings as #8 copper, except NM and UF are generally not offered in aluminum, so it's good for 50A.

"Other types" of /3+ground cable are hard to find... but in conduit country, you aren't meant to put cable in conduit, you use individual wires such as THHN or XHHW. They are allowed the higher ampacity.

Aluminum is fine for large feeder, just not for this

Apprehensions about aluminum generally are misplaced. If you knew the full story of aluminum wire, you'd cast the blame in quite different places; and in fact you'd run out and buy a torque screwdriver! But that aside...

Aluminum is not a good fit when the terminations are not rated for aluminum. So look at your range receptacle. If it is UL-listed for aluminum wire, then you're all set.

At the breaker end, it's not a problem; during the aluminum backlash they examined everything, and the standard for breaker connections passed, and that UL standard did not need to be revised.

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    +1 For this answer, in addition I would exhort you to not leave a weak link in the infrastructure of your kitchen renovation. If you can't use an existing conduit route at least route new cable from the kitchen to the panel if you can. Even the Leviton $9 range receptacle on Amazon is listed for aluminum. 4-4-4-6 Al ser is currently $1.47/ft platt.com/platt-electric-supply/… Jun 1 at 2:21
  • @NoSparksPleae good point, edited. And aluminum gets better: if it's not NM or UF, then you can get 50A out of #6Al. Jun 1 at 3:19
  • After getting into replacement of the service panel , there are 4 wires for both dryer and range.3 wires are connected on dryer, why I don't know. Will fix that.
    – Ken
    Jun 5 at 17:23

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